Kiln tyre is the most important supporting part of rotary kiln. It not only bears all the weight of the kiln shell, but also plays a reinforcing role on the thin-walled cylinder. Therefore, in the actual processing process, the quality requirements are strict. It is a serious accident of rotary kiln equipment that the tyre of rotary kiln tyre is cracked or fractured.
The fracture of rotary kiln shell is very rare, but once it happens, the cause must be found out in time to solve the problem, so as to avoid causing more losses. According to the mechanical engineer of REAMOR INDUSTRY, after the fracture of the rotary kiln tyre, the samples of the broken part should be sent to the professional organization or manufacturer for further quantitative analysis of the causes of the tyre fracture accident, including fracture analysis, material chemical composition analysis, mechanical property test, hardness test, etc.; finally, a detailed analysis report is given.
Rotary kiln shell usually has the following conditions:
1. The cylinder under the tyre has necking phenomenon in different degrees, and the continuous operation will easily cause cylinder fracture.
2. The cylinder body at the intersection of cooler and rotary kiln discharge port is prone to fracture accident.
The fracture of rotary kiln shell usually has many forms
1. The cracks are distributed along the circumference of the cylinder section, accompanied by the bending of the cylinder.
2. Once the crack exceeds 1 / 3 of the perimeter of kiln circle, it is possible to cause cylinder fracture accident.
The reason analysis of rotary kiln shell fracture is as follows
1. The overall strength is low. At the intersection of the cooling drum and the kiln discharge mouth, several multi barrel cooling machine blanking holes are evenly distributed on the circumference of the cylinder, so that the length of the actual iron plate is only about 1 / 2 of the circumference of the circle, and the overall strength is obviously reduced, so it is very easy to fracture.
2. Groove marks are formed in the process of manufacturing, transportation and installation of rotary kiln cylinder, which leads to micro cracks. After cracks appear, rush repair is necessary. However, in the process of emergency repair, if the welder’s welding technology is not up to standard, or the welding filler metal is not selected properly, the welded parts are easy to crack again and extend, resulting in cylinder fracture accident.
3. Under high temperature condition, the cylinder is subject to alternating load and cold and hot changes for a long time. When the kiln is shut down due to production or non production reasons, radial deformation of the cylinder section may occur. The thermal calibration of rotary kiln shows that the surface temperature of the cylinder is often higher than 300 ℃. In this high-temperature working environment, especially the alternation of cold and hot, it is easy to lead to the fatigue of the steel plate material of the rotary kiln, the decrease of the rigidity and the fracture.
If there are cracks in the source area of kiln shell fracture before fracture, after repair welding, but the welding quality is poor, the initial crack cracks longitudinally along both sides of the repair welding, extends to both ends for a certain length, then bifurcates, and gradually turns to expand in the circumferential direction under the action of gravity until the cylinder breaks and falls off the lower kiln platform. Kiln shell is a kind of low temperature brittle fracture which is produced on the basis of large-scale defects. Under the condition of low material temperature, the rapid brittle fracture occurs directly under the dynamic load. Before the final low-temperature fracture, the defects have experienced the expansion process of corrosion damage, hot welding damage and crack fatigue.
The reason for the fracture of the rotary kiln shell is that the oxidation corrosion of the rotary kiln cylinder is too large, the base metal of the cylinder becomes thinner, especially at the tyre part, the gap between the base plates is small, the cooling air can not blow in, and the cylinder under the tyre can not be fully cooled, resulting in local high temperature oxidation corrosion.
The excessive sulfur and phosphorus in the flue gas accelerates the oxidation of the base metal of the cylinder, which changes the temperature requirements for hot and cold brittle cracking. When the corrosion of the base metal of the cylinder is thinned to a certain extent, brittle cracking occurs at high temperature. Due to the fact that the crack position at the kiln body tyre is in the vertical upward position when the ignition temperature rises on the same day, the gravity action of the kiln end section in the heating process, in addition to the low temperature and excessive phosphorus, causes the steel cold brittle temperature to rise, causing the crack to expand to the kiln tail, which is affected by the gravity of the kiln end section, and cracks rapidly until fracture.